What symbols/characters are not allowed in tags?

Question

What symbols/characters are not allowed in tags?

Answer 1

What characters are allowed in tag names?

Always allowed

• lowercase Latin letters a to z
• digits 0 to 9

Conditionally allowed

• plus +
  • single plus allowed at the end of tags: gdi+, com+, im+ (query)
  • double plus ++ allowed anywhere except the start of a tag: c++, visual-c++-2010, g++4.8 (query)
• hyphen -
  • allowed anywhere except the start or end of a tag: objective-c, ruby-on-rails, sql-server (query)
• number symbol (hash) #
  • allowed anywhere except the start of a tag: c#, f#-interactive, c#-to-f# (query)
• period .
  • allowed anywhere except the end of a tag: .net, .htaccess, python-2.7 (query)
• accents ã and foreign language ム
  • Certain non-English sites allow special language specific characters
  • Examples: Stack Overflow in Russian, Portuguese, Spanish, Japanese

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Related Questions

• Tag names cannot end with hyphen (-)
• Bug with tags with plus in name
• How can I create a tag that contains "+"?

Answer 2

On the sidebar it says that these are the Tag Characters:

Tag characters: [a-z 0-9 + # - .]

I'd assume anything not listed there is invalid.

Answer 3

At least for chat room tags I was just able to create a tag español for the Spanish chat room. I thought the system would automatically change it to espanol like it does for the question tags. So I went further and tried to create a 日本語 for the Japanese chat room, but it got converted to ???.

So the answer may be:

• Some Latin-1 characters are no longer disallowed

or

• That subsets of characters not allowed in question tags is different to that not allowed in chat room tags

or

• There's a bug in chat room tags that allows you to use characters that are not supposed to be allowed